Home Studio Acoustics 101. Section 1. The Basics.

I realize that this post series might not interest many of our usual readers but I’ve been thinking about writing this for quite some time and I will keep it light. Acoustics is a science and there are actual degrees awarded in the subject. A lot of what is spoken of here is heightened to higher levels in commercial studios. This series of posts however is intended to give general advice for the ever growing home studio environment and I am no means an expert on the topic. Enjoy!

Most do not understand what makes a “recording studio” suitable for recording. Obviously to most there is the equipment such as microphones, cables and recorders (computers and software programs these days), but one of the most important elements (besides a great band) to a great sounding recording is a great sounding room.

What does that mean? Well, that means that the “room acoustics” or the way a room responds to the sound within the room is pleasing and or controlled. When you open your closet door and talk, it sounds different. When you are in a large room with hard floors, walls and ceilings, you can hear more of the “room” and it’s largeness. Your brain was created to be able to recognize the basic size of a room without you having to see it. Pretty cool huh!

BASIC CONCEPTS OF SOUND

“Sound is a result of the pushing and pulling of air molecules.” The audio spectrum is broken up into measurable frequencies from 20Hz (very, very low) to 20,000Hz (very, very high) and everything we humans hear resides in this range.

The fundamental or root frequency producing the “boom” of a kick drum sound is around 75Hz. The “shick” of a shaker is about 4,000Hz. That annoying tone you hear in the Emergency Broadcasting Tests is pure tone of 1000Hz (or 1KHz). These frequencies and their associated waveforms push and pull air molecules while interacting with their harmonic frequencies (multiples of the fundamental) and the room on a path to your ears. Your ears contain frequency specific tiny hair-like receptors (cilia) that then take that acoustical energy and transduce (or change) that energy into electrical impulses that your brain perceives as “sound”. Amazing huh?

Ever wonder why it’s really only the bass you hear from the car behind you at the red light? Bass (low) frequencies are physically longer that those higher in our audible spectrum. The length of the frequency (wavelength) is derived by taking the speed of sound (1130 feet per second at 68 degrees) and dividing it by the cycles (positive “push” and negative “pull”) per second. This means that the physical wavelength a low frequency such as 100Hz is nearly 11.5 feet long! A very high frequency like 10,000Hz (or 10KHz) is less that 1.5 inches. You hear the bass frequencies further than their counterparts because they are physically longer and therefore travel further. In the same sense, the intimacy of a whisper is identified by the detailed high frequency “spit” noises that accompany the proximity of another’s mouth. Moving further from the whisper loses that detail. Cool huh?

In a studio it’s imperative to control the sound to help “clean up” whatever you are trying to record or hear. Due to the physicality of sound and its behavior in a room or “the acoustics”, this can be tricky to accomplish. Ever notice that in some spaces like a standup shower, that some notes you sing resonate with more intensity than others? This is due to the physical length of the frequency and the physical dimensions of that space “fitting” together. Drums along with the tuning of their heads are intentionally designed with specific dimensions to make these resonant frequencies accomplish the desired tone. Sometimes this interaction is negative (null), sometimes its positive (node). While entertaining in concept, these interactions can really mess up recording or listening space.

Some of these issues can be avoided in construction. Non-parallel surfaces (wall to wall and ceiling to floor) help eliminate the inherent “standing waves” or resonant frequencies of the room because the waveform is reflected off at a different angle and path than which it traveled. Most commercial studios are engineered and designed in this manner. For the home studio/listening room or theater, the best way this is achieve a good sounding room is to control the way the sound interacts within the space you have. This can be achieved by using physics to our advantage by making surfaces non-reflective or at least non-reflective on the same plane. This introduces the concepts of absorption and diffusion. But before we go there though, lets talk about ISOLATION, a key element to a quite space.